1. Field of the Invention
The present invention relates to a printed board for a filter used in various electronic devices, and a filter formed by mounting a chip-type solid electrolytic capacitor on the printed board.
2. Background Art
In response to the increase in frequencies of electronic devices, there has risen a demand for a capacitor, as one type of electronic component that has a high impedance characteristic in a region of a frequency higher than that in a conventional capacitor. In order to meet such demand, various solid electrolytic capacitors containing conductive polymer of high electric conductivity as a solid electrolyte have been developed. Such solid electrolytic capacitors have large capacitance, so that they are used in π-type filters for cutting high-frequency components in signals.
FIG. 5 is a top view showing a wiring pattern of a printed board for forming a conventional filter employing a chip-type solid electrolytic capacitor. FIG. 6 is a front view of a mounting surface of the chip-type solid electrolytic capacitor to be mounted on the printed board. FIG. 7 is a top view showing a state where the chip-type solid electrolytic capacitor and a chip inductor are mounted on the printed board.
Printed board (hereinafter referred to as “board”) 60 has pattern 61 through pattern 64. Chip inductor 65 is mounted between pattern 61 and pattern 62. Chip-type solid electrolytic capacitor (hereinafter referred to as “capacitor”) 50 has a four-terminal structure. Capacitor 50 includes a plurality of capacitor elements (not shown), and these capacitor elements are divided into two groups. Positive electrodes in one group are connected to terminal 51, and positive electrodes in the other group are connected to terminal 52. Negative electrodes of these capacitor elements are connected to terminals 53 and 54. Terminal 51 is connected to pattern 61, terminal 52 is connected to pattern 62, terminal 53 is connected to pattern 63, and terminal 54 is connected to pattern 64. Thus, a π-type filter is formed. Equivalent series inductance (ESL) of capacitor 50 is reduced by such a structure.
In the conventional filter, capacitor 50 and chip inductor 65 are combined and mounted on board 60. In order to improve the high frequency-cutting property of the π-type filter, large chip inductor 65 is required. Mounting such chip inductor 65 occupies the area on board 60. Therefore, it is difficult to downsize the π-type filter.